Various types of electron discharge electrodes and devices (hereinafter, referred to as "electron discharge device") have been known and used in the art of discharge and light-emitting. There are two types in such an electron discharge electrode: a thermal electron source, and a cooled cathode electron source. As such a cooled cathode electron source, a field emission type (FE type) electron discharge device, a metal/insulator/metal type (MIM type) electron discharge device, and surface transmission type electron discharge device have been known.
With respect to an MIM type electron discharge device, Mead indicated that a device such as Al--Al.sub.2 O.sub.3 --Al, Ta--Ta.sub.2 O.sub.5 --Au, and so on operated as a vacuum emitter. The MIM type electron discharge device discharges electrons when tunnel electrons pass through an insulation film (I) such as Al.sub.2 O.sub.3. This device, however, cannot enjoy discharging stably with high efficiency, and may suffer from insulation breakdowns due to a highly biased electric field for discharging electrons, thereby raising a problem in stability of the device itself, so that such a device is still not be used practically.
It is an object of the invention to provide a novel structured electron discharge device for discharging electrons in utilizing the tunnel effect but hardly suffering from insulation breakdowns otherwise caused by the bias voltage and a method for discharging electrons using this device.